Colorado River flows to drop 10 percent, study projects

Colorado River flows are likely to shrink by 10 percent in coming decades as the climate warms, according to a recent study in the journal Nature Climate Change.

The study, published Dec. 23, examines the relationship between rainfall and evaporation on surface water throughout the Colorado River basin, said Richard Seager, a climate scientist at Columbia University’s Lamont-Doherty Earth Observatory and lead author of the study.

Although climate change is an evolving field with varied estimations on the rate of change, the study draws on 16 different climate models. It projects that temperatures in 2021-2040 will be 1.8 to 3.6 degrees Fahrenheit warmer than they are now.

The hotter air is likely to increase rain in the river’s headwaters during that period, but annual stream flow will decline by an average of 10 percent, and by up to 25 percent during springtime, as warmer temperatures boost evaporation, the study projects.

Northern California will likely see greater rainfall in winter, but also increased evaporation, leading to an overall loss in surface water, the study found. Southern California is expected to get both dryer and hotter and spring runoff throughout the state is projected to drop by 20 percent.

The Colorado provides water for 40 million residents, is used by millions of businesses and irrigates 5.5 million acres of farm land and generates electricity for cities from Las Vegas to Los Angeles. It is also a critical source for fish and wildlife, as well as national parks. San Diego typically receives more than half its water from the Colorado.

Spanning seven states from Wyoming to California, the river system is in a 12-year dry spell, and demand for its water are expected to outstrip supply in coming decades, according to a recent federal report on the basin.

Moreover the region’s population is expected to grow by nearly 10 million more residents by 2060, increasing demand on the water supplies. The projections offer starting point for management of the decreased flows, Seager said.

“It may not sound like a phenomenally large amount except the water and the river is already over-allocated,” Seager said.